1. Field of the Invention
The invention relates to methods and compositions for increasing the adhesiveness of grease repellant papers and more particularly to the use of styrene/butadiene rubber emulsion as a priming system.
2. Brief Description of the Prior Art
Paper containers used in the packaging industry for distribution and storage of food products are commonly made with paper that has been treated with a fluorocarbon sizing agent that makes the paper grease-repellant. This prevents wicking or staining that occurs on non-treated papers with high grease or high fat content products, such as for example, pet foods. Paper thus treated with the fluorocarbon material becomes resistant to hot melt adhesives applied for the purpose of bonding paper to paper closures. The sealing must be such that assures strong closures and presents product siftage.
Paper to paper bonding with good shear, peel and tearing properties of such containers is of considerable industrial importance and consequently there is a great deal of work done in this area of technology. For example, U.S. Pat. No. 3,313,218 describes a method for joining waxed paperboard surfaces whereby glue is heated to an extremely high temperature before application to the waxed surface. In this method, the super-heated glue melts the wax, allowing for adhesion of the two waxed surfaces. In other prior art methods, a claycoat is used for improvement of adhesion of grease resistant surfaces.
The present invention is an improvement over prior art methodology in promoting both good sealing and fiber tear properties without resort to drastic conditions, such as the use of very high temperatures. The method consists of first priming the surfaces to be sealed with an emulsion of butadiene/styrene rubber, (SBR), and then applying a hot melt adhesive.